Three’s Company? Prioritizing Trilateral Deterrence Against North Korea

16985509420_3dd3834007_3k (1) (1)

In December 2018, a South Korean destroyer allegedly locked its targeting radar on a Japanese surveillance aircraft. Although details of that incident remain bitterly contested, the controversy captures well the suspicions and ill-will that have engulfed Japanese-South Korean relations. The tarring of that military-to-military relationship — one that has historically served as a shock absorber for difficulties between the two governments — is particularly troubling for the United States. The challenge of deterring a nuclear-armed North Korea is more severe if its two closest allies in Northeast Asia are more concerned about each other than their common adversary.

The extent of that challenge has long occupied U.S. strategists and planners. Days after the 2016 election, President Barack Obama warned his successor Donald Trump that North Korea would be the most urgent threat he would face. Much has changed since then, but North Korea remains one of the most pressing security challenges as President Joe Biden returns to the White House.



North Korea’s nuclear threat has not remained static over the last four years. It continued to build a larger and more capable arsenal to menace its neighbors and hold U.S. cities at risk. As Vice Chairman of the U.S. Joint Chiefs of Staff Gen. John Hyten said last year, North Korea is “building new missiles, new capabilities, new weapons as fast as anybody on the planet.” Pyongyang is now positioned to test U.S. alliances in Northeast Asia like never before.

The lack of meaningful trilateral cooperation between the United States, Japan, and South Korea makes deterring North Korea more difficult. Pyongyang is poised to exploit gaps between Washington, Seoul, and Tokyo. It has signaled for years how it would do so: by using nuclear threats against Japan to weaken U.S. resolve to defend South Korea and Japanese willingness to grant the United States use of bases on its soil that are critical for responding to a Korea contingency. North Korea’s growing capabilities make those threats too dangerous to ignore.

Trilateral deterrence on the part of the United States, Japan, and South Korea should be a pillar of, not a supplement to, U.S. strategy toward North Korea. Successive U.S. administrations have pushed for trilateral cooperation, only to see their efforts stymied by domestic politics in South Korea or Japan. Getting Seoul and Tokyo to work together is no easy task. Failure to do so, though, threatens the security of all three countries. Fortunately, there are signs that South Korean and Japanese leaders are both alert to the need for greater cooperation and prepared to begin a constructive dialogue toward improving relations. U.S. leadership will be necessary to bring the two allies into a deterrence partnership. The Biden administration has signaled it is ready to fill that role.

We offer a set of recommendations to move the three governments toward an operational framework to meet the deterrence requirements of a new era: trilateral presidential-level summitry to set a direction and provide much-needed momentum for cooperation; the inclusion of allies throughout the Biden administration’s North Korea strategic review process, not just at the beginning and end; the establishment of a trilateral deterrence policy dialogue; the creation of a mechanism to enable nuclear-related consultations during crises; standing up a planning capability to better coordinate conventional operations under the nuclear shadow; and strengthening alliance contributions to U.S. strategic deterrence missions.

Beijing is sure to object to any measure the three countries take to strengthen regional deterrence. Although the trilateral framework outlined below is tailored to North Korean threats, it could be broadened to meet Chinese aggression. Ideally, China would apply pressure to restrain North Korea in a way that precludes the need for such trilateralism. Until that time, however, the allies cannot leave themselves vulnerable to North Korea to appease Beijing.

North Korea’s Evolving Nuclear Threat

North Korea has substantially increased the size, diversity, and sophistication of its nuclear arsenal over the last decade and there is no sign that it will ease up on that mission. According to some estimates, it now has enough fissile material to build well over 50 warheads and can add around 10 weapons’ worth to its stockpile every year. It has continued to unveil and test new missiles to deliver those weapons on targets across the globe, including advanced designs that are intended to evade missile defenses. During a parade in October 2020, North Korea rolled out a “monster missile” — what appeared to be the world’s largest road-mobile intercontinental ballistic missile. Earlier this year, Kim Jong Un committed to fielding solid-fueled, intercontinental ballistic missiles fitted with multiple warheads, submarine-launched capabilities, as well as tactical nuclear weapons.

North Korea’s statements, capabilities, and past nuclear exercises that it advertised as trial runs for “preemptive strikes” against airfields and ports in South Korea and Japan portend a dangerous shift in its nuclear strategy. While it may be close to possessing viable retaliatory capabilities, it is already developing options toward a warfighting strategy — a strategy to enable limited nuclear strikes on regional targets, while using threats against multiple U.S. cities to deter an overwhelming U.S. response. Kim Jong Un made clear in his 2017 New Year’s address that retaliation is no longer the sole tenet guiding North Korea’s nuclear strategy, when he said: “we will continue to build up our self-defense capability, the pivot of which is the nuclear forces, and the capability for preemptive strike.”

North Korea’s history of nuclear threats in combination with lower-level provocations suggests it may believe it can use, or threaten to use, those weapons to coerce — not just deter — the United States and its allies. While it is hard to imagine North Korea would ever conclude that it could use nuclear weapons against the United States or its allies and survive, it is not immune to misperception or miscalculation. All national leaders are subject to the perils of misperception, but experts suggest dealings with North Korea are singularly prone to such problems. The United States and its allies cannot afford to send muddled messages, especially when it comes to deterrence.

Trilateral Cooperation: A Yawning Deterrence Gap

The new administration faces two imperatives when it addresses North Korea policy. The first is identifying anything that can be salvaged from the Trump-Kim summits that it can use to push for “principled diplomacy” to restrain or reverse North Korea’s nuclear program. Such an approach might include reaffirming the principles set out in the 2018 Singapore Joint Statement committing both sides to build a workable agenda for denuclearization negotiations. Recognizing that a deal for complete denuclearization is unlikely to materialize in the near term, the Biden team might, as Ariel Levite and Toby Dalton advocate, opt for a phased approach that starts with limiting North Korea’s ability to build new and more advanced weapons. Regardless of the approach to negotiations the Biden team adopts, North Korea’s existing capabilities are likely to remain in place for the foreseeable future. That is where the second imperative comes in: upgrading the U.S. regional deterrence and defense posture that has been largely neglected in recent years even as North Korea’s nuclear capabilities have grown.

Urgent attention is needed to repair U.S. bilateral relationships with South Korea and Japan, particularly as it relates to America’s nuclear guarantee. Trump’s transactional diplomacy, especially for allies, has eroded the core requirement for maintaining a credible extended deterrent: perceived U.S. resolve to defend allies against nuclear threats, even at risk to the U.S. homeland. The new administration has already prioritized rebuilding relations with, and underscoring U.S. commitments to, its Northeast Asian allies. Reports suggest the first overseas travel for U.S. Secretary of State Antony Blinken and Secretary of Defense Lloyd Austin will be to Japan and South Korea later this month. And, Biden’s first in-person visit with a foreign leader will be with Japan’s Prime Minister, Yoshihide Suga, in April. Early engagements with Northeast Asian allies would signal a prominent place for the region in Biden’s strategic outlook.

A growing and potentially more challenging deterrence problem stems from the sorry state of trilateral security cooperation among the United States, South Korea, and Japan. North Korea may be pursuing a “triangular decoupling strategy” by putting Japan first on its nuclear target list, reasoning that threatening Japan will present the United States with a strategic dilemma: Will it sacrifice one ally in Tokyo to save another ally in Seoul? Alternatively, Pyongyang may hope that it can convince Japan to deny the United States the use of bases on its soil for the defense of South Korea, complicating the flow of U.S. forces to the peninsula during a crisis.

Put bluntly: If North Korea believes it can split the alliances with nuclear threats, deterrence will be weakened. Pyongyang will be emboldened to use force or the threat of force to challenge what it contends to be objectionable political, military, or territorial arrangements. War is more likely if it misreads U.S. and/or South Korean resolve in the face of such a challenge. And North Korea’s modernizing capabilities mean that the destruction would be felt far and wide, perhaps including nuclear attacks on U.S. cities. The stakes for deterrence are high and growing.

The Biden administration should make trilateral security cooperation a pillar of its deterrence strategy toward North Korea. U.S. policymakers have long argued that trilateral cooperation is valuable, but they have often treated it as a supplement to the bilateral alliances — something extra. That framing is outdated. Trilateral cooperation is no longer a luxury. North Korea’s nuclear developments require the United States to demand from Seoul and Tokyo such cooperation as essential to effective deterrence. Moreover, allied military capabilities have matured. They are able to do more than ever before to contribute to deterrence. This recognition provides the foundation for new thinking about burden sharing among allies and the reconfiguration of U.S. alliances in Northeast Asia to strengthen deterrence beyond recommendations to assure allies of U.S. nuclear commitments.

From the Top: Setting the Right Tone and Direction

Getting South Korea and Japan to work together will not be easy. History looms large in both countries, but especially in South Korea, and strategic concerns are often subordinated to domestic politics. The memory of Japanese occupation of the Korean Peninsula in the first half of the 20th century has consistently derailed efforts in Seoul to improve relations with Japan. Recent public opinion polls show South Korean views toward Japan are at a near all-time low, and Japan is seen by many South Koreans as a future security threat. Japanese views toward South Korea are similarly grim and there is little public support for measures that might improve the bilateral relationship, even as leaders in both countries acknowledge their importance in the abstract.

Biden has already sent reassuring messages to U.S. allies, and many experts expect him to play a helpful role in mending ties between South Korea and Japan. However, his administration should set its sights higher than merely smoothing over troubled relations between the two allies. While Washington cannot solve the disputes that roil the Seoul-Tokyo relationship, it should communicate to them that their continuing deterioration of relations — or even the current paralysis — is unacceptable. It should articulate a vision for regional deterrence and defense that makes clear the stakes and a potential price to alliance relations for continued indulgence of historical grievances. In short, the United States should make clear to its allies that it cannot act effectively in defense of their national interests if they cannot work together. The stakes for the United States have changed and business as usual in the face of North Korea’s growing capabilities diminishes the security of each country.

The Biden team should bring South Korea and Japan fully into its strategy reviews of the North Korean nuclear threat and seek to adjust the regional security architecture to reflect four new realities. First, North Korea’s nuclear weapons are here to stay for the foreseeable future. While denuclearization remains a diplomatic priority, Pyongyang is unlikely to abandon its nuclear ambitions any time soon. Second, North Korea is signaling that any war on the peninsula will be a nuclear one. It can no longer be assumed that it would use nuclear weapons only in the dying throes of the Kim regime. Third, the potentially catastrophic consequences of a second Korean War would not be confined to the peninsula. It must be presumed that North Korea can and will make good on its threats against Japan and the United States. Lastly, an effective deterrence posture requires a coherent and robust trilateral approach.

The strategy review process should be bookended by trilateral presidential-level summitry. The first meeting at the earliest possible date would acknowledge the need for and set-in motion a trilateral, two-track approach toward North Korea. The first track would include a commitment to diplomacy that advances both denuclearization goals and inter-Korean peace. The second track should emphasize a commitment to strengthening trilateral deterrence and response capabilities against North Korea’s growing threat in the event that denuclearization diplomacy falters. The second summit would announce the findings of the review and the strategy that it created.

South Korea and Japan should not bear the burden of adjusting to trilateralism alone. The United States should be prepared to adapt its plans, force structure, and investments to ensure they are well-suited to support the trilateral requirements for deterring and responding to North Korea’s growing nuclear threats. It should be ready to bring allies more fully into policy and planning processes, including those related to nuclear crises and war, in ways that will be uncomfortable at first. All parties need to hone their understanding of deterrence and its requirements, the implications of deterrence failure, and the response options that may need to be considered if North Korea employs nuclear weapons. This requires a more inclusive approach. Including allies in the review process signals U.S. readiness to do its part.

Operationalizing Trilateral Deterrence

Trilateral summits, ministerial meetings, and strategy documents are necessary for setting the right direction, but they should also directly enable concrete action to build and strengthen trilateral deterrence. Below are options to jumpstart the kind of coordination and cooperation that is necessary for deterring North Korea in a new era.

The vital first step is an early trilateral summit that signals a commitment to a positive outcome at the highest level of all three governments. This affirmation is needed to motivate lower-level officials. We don’t doubt those officials’ readiness to cooperate, but their inboxes are full and there is much to do given new administrations in Washington and Tokyo. Presidential and prime ministerial approval can provide much needed prioritization, momentum, and direction.

Establish a Trilateral Deterrence Policy Dialogue

A second step is to establish a trilateral deterrence dialogue to advance a common understanding of the threat, deterrence requirements and expectations should deterrence fail, and areas for improved policy coordination. The existing bilateral deterrence dialogues the United States maintains with South Korea and Japan are essential to support the goals, military relations, and political consultation mechanisms that are unique to each alliance. But, because they are bilateral, they are insufficient for deterring a North Korea committed to exploiting perceived gaps between the two alliances. A trilateral dialogue should not replace existing bilateral dialogues — it should strengthen them. Its scope should be broad to include the full range of threats — conventional, chemical, cyber, as well as nuclear — to enable the development of a coherent deterrence posture that accounts for escalation risks across the entire spectrum of possible North Korean provocations.

Create a Nuclear Consultation Mechanism

An early goal of the new dialogue should be to establish a trilateral mechanism tailored explicitly to enable nuclear-related crisis consultations among national leaders. Former Deputy Assistant Secretary of Defense Brad Roberts argues that the absence of such a mechanism “is perhaps the biggest gap in the existing deterrence architecture and promises to become even more glaring as the threat [from North Korea] develops.” Should any scenario emerge in which the U.S. president is considering the employment of nuclear weapons to defend an ally, it is difficult to imagine that he would not seek input from leaders in Seoul and Tokyo, who would rightly expect to be consulted if time and circumstance permit. Waiting to adopt a mechanism ad hoc during a time of extraordinary stress, in which every minute lost could have grave consequences, is no way to prepare U.S. and allied leaders for the most consequential conversation they might have. Preparation and extensive advance work are necessary to facilitate timely and informed decision-making in a time of a nuclear crisis. Concerns that establishing such a mechanism could create a “slippery slope” toward allies believing they need a more robust U.S. nuclear presence or need to build their own weapons notwithstanding, doing otherwise is a recipe for alliance failure.

Enhance Trilateral Planning for Conventional Operations Under the Nuclear Shadow

Whereas a nuclear consultation mechanism would enable national leaders to dialogue during a crisis in which a U.S. president may consider employing nuclear weapons, steps are also needed to coordinate operational-level planning against a nuclear-arming North Korea. We recommend standing up a trilateral planning capability to sustain attention on the operational implications of a North Korean nuclear attack, as well as mitigation and response options. This would involve the relevant allied planners to enhance conventional military — not nuclear employment — operations and coordination under the nuclear shadow.

This conventional focus distinguishes our recommendation from one that was made in a recent task force report from the Chicago Council on Global Affairs. That report calls for establishing an Asian Nuclear Planning Group, similar to NATO’s long-standing nuclear planning group. It would bring Australia, Japan, and South Korea “into U.S. nuclear planning processes and provide a platform for these allies to discuss specific policies associated with U.S. nuclear forces and conduct war games and exercises, including those involving the highest political-level participation.” The Chicago Council recommendation is likely to face two near-term obstacles. Stout anti-nuclearism in Japanese politics is likely to prohibit it from joining a group tasked explicitly with nuclear employment planning. Moreover, by including Australia, an Asian nuclear planning group would appear, to Beijing at least, to be aimed at China, complicating South Korean membership. What we recommend is a trilateral mechanism that can be easily tailored to — and explained to domestic constituencies as — responding to a clearly growing North Korean threat and is focused on better enabling conventional operations in a nuclear environment.

Defense communities in all three countries have long recognized the need for greater information sharing and coordination to support critical missions, such as noncombatant evacuation operations and missile detection and defense. Also sorely needed is deeper consideration in planning for Japan’s involvement in a Korean contingency. Japan could provide medical and humanitarian support to mitigate the consequences of a North Korean nuclear attack on the South, substantial anti-submarine and maritime defense capabilities for operations in the Sea of Japan, and use of ports/bases located on its territory by both U.S. and South Korean forces to enhance resiliency should nuclear strikes on military targets in South Korea render bases there inoperable. These are difficult but necessary conversations to have, and they are not going to get any easier, as the nuclear (first strike) threat to Japan grows. Sober discussions about the effects of a nuclear exchange on conventional military operations could inject a greater sense of realism into allied investments, planning, and exercises to enhance their ability to communicate, operate, and deny North Korea benefits from using nuclear weapons against allied forces.

Some in the defense communities of all three countries may object to a trilateral planning mechanism due to the classified nature of military plans. To be clear, this is not a call to strip unilateral or bilateral plans of their classification to share them with partners. Engaging in planning is not the same thing as sharing plans. Savvy planners can have informed and useful discussions about the operational implications of a nuclear attack and response options without divulging information beyond a given level of classification. Those discussions can lead to the development of better-informed unilateral and bilateral plans and facilitate timely operational-level coordination, if needed.

Strengthen Allied Contributions to U.S. Deterrence Operations

Lastly, recent changes in U.S. regional bomber operations provide a need and rationale for strengthening allied involvement in U.S. strategic deterrence missions aimed at North Korea. In April 2020, the United States stopped permanently basing strategic bombers in Guam. The official explanation emphasized the need to adopt a “dynamic force employment” concept that was introduced in the 2018 U.S. National Defense Strategy, which prioritized expanding the flexibility of U.S. regional deployments. The United States now relies solely on continental U.S.-based bomber groups that can deploy to different locations in the region at a time of their choosing for deterrence missions.

The new approach arguably increases the resiliency and flexibility of the bomber force but it has raised doubts about the U.S. commitment to regional security. In an apparent effort to assuage some of these concerns, the U.S. Air Force Global Strike Command has said it “will maximize all opportunities to train alongside our allies and partners, to build interoperability, and bolster our collective ability to be operationally unpredictable.” When it comes to missions aimed at deterring North Korea, the focus should be on finding and exploiting opportunities to enhance trilateral cohesion.

The United States conducted bomber overflight missions in response to North Korea’s 2017 intercontinental ballistic missile launches. South Korean and Japanese fighters provided tactical escorts, offering a particularly strong show of unity. Should an uptick in tensions with North Korea resume, routinizing combined exercises of this nature could help demonstrate alliance resolve. Moreover, the transition to a “dynamic force employment” model is intended to allow U.S. bombers to operate from a “broader array of overseas locations.” Joint allied investments in airfields to expand that range of potential locations from which U.S. bombers can operate, potentially including on allied territories, would signal a combined commitment to U.S. strategic deterrence operations against North Korea.

Anticipating the China Factor

Hanging over many of these discussions is China. While the approaches outlined above are narrowly focused on the threat from North Korea, Beijing is nonetheless likely to take offense. It has a history of objecting and responding with punitive measures to actions the United States and its allies take to protect themselves against North Korea. And it may see in stronger trilateral cooperation against North Korea a harbinger of alignment against it.

The scope of trilateral cooperation indeed could be broadened to better cope with an expansionist China. Optimistically, that specter of trilateral deterrence would encourage Beijing to apply more pressure to restrain North Korea. At the end of the day, Chinese sensitivities and potential reactions should not discourage the allies from adopting necessary measures to enhance deterrence and defense against North Korea. However, the allies could take measures to be transparent that trilateral cooperation is not aimed at containing China. Ultimately, in this and in other areas, Beijing should not have a veto over policies the United States and its allies deem necessary to their national security.

Final Thoughts

Unlike changes in force posture or nuclear signaling to strengthen deterrence, creating a trilateral deterrence dialogue, a nuclear consultation mechanism, and a conventional military planning capability have the benefit of not overtly raising military pressure on North Korea. They do not include an outward show of force. As a result, they could be adopted in the near term without being seen by Pyongyang as provocative in a way that disrupts the diplomatic agendas of either Washington or Seoul. Rather, they establish a framework to enable a sound trilateral response should diplomacy falter. Efforts to strengthen allied contributions to U.S. strategic bomber missions, however, fall in another category. Because they may be seen as militarily provocative by Pyongyang, those measures could be discussed now but implemented at a time of the allies’ choosing.

Lastly, vital to these efforts will be a public information program that explains to the three publics the necessity and value of trilateral cooperation. This will be a difficult task, not only because it demands that speakers go straight to the maw of historical grievance, but also because it concerns straight talk about nuclear war, a subject that most governments prefer to avoid. Yet it is only by acknowledging the potential implications of crises and deterrence failure that countries can signal the resolve that is a critical element of deterrence. Vision and leadership will be essential. Without this, deterrence will weaken and could fail.

The governments in Washington, Tokyo, and Seoul have long acknowledged that a forward-looking, cooperative relationship among them is a pillar of their defense strategies and is essential to any effort to deter and, if necessary, defeat an adversary in the event of a crisis or conflict. In recent years, however, domestic political considerations have outweighed that national security imperative. Such self-indulgent thinking is ever more dangerous. There is now an opportunity to return to first principles, resume and advance trilateral cooperation, and strengthen deterrence in Northeast Asia. The visits to Japan and South Korea later this month that are reportedly being planned for Secretaries Austin and Blinken offer a chance to get started.



Shane Smith is a senior fellow at the Center for the Study of Weapons of Mass Destruction at the National Defense University. He has served as Senior Advisor for East Asia Nuclear Policy in the Office of the Secretary of Defense and as a senior adviser at the Defense Threat Reduction Agency. The views expressed are those of the authors and are not an official policy or position of the National Defense University, the Department of Defense or the U.S. government.

Brad Glosserman is deputy director of, and visiting professor at, the Center for Rule Making Strategies at Tama University in Tokyo, as well as senior advisor (nonresident) at Pacific Forum. He is the author of Peak Japan: The End of Great Ambitions (Georgetown University Press, 2019) and The Japan-South Korea Identity Clash: East Asian Security and the United States (Columbia University Press, 2015).

Image: State Department

CCBot/2.0 (